75 



Further evidence of this signal loss in unconsolidated sediment was documented on 

 the MQR mound. Several pockets of material on the western and southern slopes of MQR 

 showed a decrease in material hardness relative to the surrounding dredged material. 

 Disposal logs indicate that sediments dredged from Pine Orchard Harbor were being 

 deposited south and west of the CDA buoy as late as 21 May 1994, 51 days before the July 

 1994 survey activity. Again, the SACS system was detecting the unconsolidated nature of 

 the recent deposit in comparison to the older CDM layer. 



3.4.3 Sediment Acoustic Characterization System, X-Star Subbottom Profiler 

 Comparison 



SAIC utilized the July 1994 survey operations as an oppormnity to compare the 

 prototype Sediment Acoustic Characterization System (SACS) to the X-Star subbottom 

 profiler. An attempt was made to run the two systems concurrently and compare the data 

 collected from the sediment surface returns. However, a comprehensive comparison of the 

 digital data was not conducted due to the relative location of the concentrated area of X- 

 Star analysis and shortcomings of the SACS system. 



The preliminary results of lane by lane comparisons show agreement between the 

 two systems when confined to relative scales of dB (SACS) and reflection coefficient (RF) 

 for X-Star (Figure 3-36). Further comparison efforts were hampered by the differences in 

 the acoustic frequency, level of penetration, and performance in the two systems. A 

 complete comparison would require the precise calculation of acoustic signal bottom loss 

 for both SACS and X-Star. The SACS software did not record the strength of the outgoing 

 pulse from the 24 kHz transducer. Therefore, calculation of signal loss by the formula (SL 

 = OutdB - lUde) where Out is the strength of the outgoing acoustic signal and In represents 

 the known signal return strength was not possible. 



The power settings for SACS were modified for optimal performance and appear to 

 have remained constant throughout individual surveys (CLIS 1994, MBDS 1993; 

 DeAngelo and Murray 1996). As a result, the data collected with SACS remains valid, 

 although it does so within the confines of a relative signal strength scale for each disposal 

 site survey. Modifications to SACS software are currently underway to correct the signal 

 power ramping problems within the system and provide the DAMOS Program with another 

 disposal site monitoring tool. 



Monitoring Cruise at the Central Long Island Sound Disposal Site, July 1994 



